Conventionally known in the transmissive radiographic imaging of the skull is the use of a cephalostat available as an accessory for a panoramic x-ray apparatus. A radiographic image exposed with the help of the cephalostat is chiefly capable of presenting the bone structure of the skull alone as the soft tissues adjacent to the skull become overexposed, thus forming black areas in the image. However, a frequent need exists for taking such radiographic images of the skull in which also the soft tissues are well discernible. To this end, prior art has conventionally employed typically wedge-shaped soft-tissue enhancing filters, which are placed between the object being imaged and the x-ray film. These soft-tissue filters are operative with positioning arrangements that permit their use for locally attenuating the x-ray beam transmitted through, e.g., the patient's face, thus making the soft tissues discernible in the radiographic image. A problem herein is how to position the soft-tissue filters correctly so as to achieve the highest possible resolution in the radiographic image simultaneously for both the bone structure of the skull and the desired soft tissues adjoining thereto. Frequently, such radiographic images are so inferior in this respect that a number of re-exposures must be taken, which increases operating costs and subjects the patient to unnecessary doses of radiation.
For an attempt to solve the above-described problem, reference is made to FI patent 68515 (corresponding U.S. Pat. No. 4,641,336) filed by Instrumentarium Oy, Finland, in which a soft-tissue filter arrangement is described for use in the radiographic imaging of a patient's skull with the help of a cephalostat in which the patient is adjusted to an accurately determined imaging position by means of ear plugs or similar elements which comprise ear, nose and/or forehead supports permanently fixed with respect to the imaging coordinate system. This prior-art apparatus has means for adjusting the distance of the nose and/or forehead relative to the ear plug supports. The apparatus is disclosed to comprise output means of control information or a signal related to said distance to the end of adjusting the position of the filtering elements.
The above-described adjustment arrangement of filtering elements based on the mutual distance of the ear plug support from the forehead support or equivalent member is extremely confusing and clumsy to the user. Moreover, the use of fixed support/positioning means whose position is referenced to a predetermined coordinate system complicate the positioning of the patient by, e.g., tilting to an optimal position for maximal diagnostic value obtainable from skull exposures. Due to this drawback, radiographic exposures taken by means of the apparatus according to the FI patent are not always satisfactory, which results in a need for re-exposures, thus subjecting the patient to unnecessary doses of radiation and/or causing loss of the diagnostic value of the exposures. Further, the apparatus according to the abovementioned FI patent does not offer the implementation of individually variable soft-tissue filtering profiles.
Further references of the prior art related to the present invention can be found in U.S. Pat. Nos. 2,506,342, 3,755,672, 4,181,858 and 4,347,440 as well as in EP patent application 0,054,798 A1.
It is an object of the present invention to provide a novel type of soft-tissue filter apparatus capable of overcoming the above-discussed drawbacks and achieving the goals to be defined later in the text.
It is a further object of the invention to provide an apparatus with extremely simple operation, clear use, and fast learning, thus offering a high hit rate of exposures and elimination of need for re-exposures.
It is a still further object of the invention to provide an apparatus in which the patient can be positioned within the x-ray beam in a diagnostically optimal position without being restricted in any way by any fixed support means.
A nonlimiting further object of the invention is to provide an apparatus which is suited to implementing different kinds of variable soft-tissue filtering profiles when necessary.
To attain the above-expressed goals and those to be clarified later in the text, the invention is principally characterized by the apparatus incorporating a light indicator unit comprising a light source capable of projecting onto the side of the face of the patient a light marker line which is transferrable along the adjustment direction of the soft-tissue filter assembly and by said light indicator unit being equipped with a sensor of the light marker line position, said sensor's positional information being adapted in the apparatus to control the position of the soft-tissue filter element to the position relative to the patient indicated by means of the light marker line projected by the light indicator unit.
The use of the apparatus according to the invention is most straightforward and obvious as well as easy to learn, since the effective area of the soft-tissue filtering on the patient's skull region is accurately indicated by the light marker line.
In the apparatus according to the invention, the patient need not be positioned relative to a fixed coordinate system, but instead, the patient can be supported in a desired manner, also tilted when necessary for diagnostic reasons.
The invention is further capable of implementing different kinds of soft-tissue filtering profiles. When necessary, such profiles are controllable and variable in the vertical and/or horizontal direction by virtue of different kinds of sequential and/or superimposed light marker line/filter wedge element combinations.